In the course of practicing a wide variety of commercially important industrial processes, aqueous or gaseous process streams (or more generally “fluid streams”) are produced which are contaminated with pernicious quantities of mercury. Mercury is corrosive to metals and other materials within the facility where the process is practiced, and is harmful to human health and to the surrounding ecosystem. The mercury contaminants have proved to be particularly difficult to remove or reduce to acceptable levels. In order to do so, it is important to know the concentration and speciation (organically-bound, ionic, or elemental) of mercury (Hg) in the stream containing same.
An important example of the type of operation to which the present invention is directed arises in the operation of oil and gas exploration and drilling facilities maintained upon platforms in natural or other bodies of water, including so-called “off shore drilling platforms”. In conducting operations at these platforms, industrial streams are developed (often referred to as “produced water”) which by virtue of the processes conducted contain comparatively large quantities of mercury, present in the form of the three species mentioned above. Such a produced water stream is exemplified herein as an aqueous system to which the invention is directly applicable, but it will be understood that the invention is in no way so limited, but may be used with a large variety of other industrial streams that have become contaminated with mercury during or as a result of the industrial process, or even more generally with any aqueous system which is contaminated with mercury in the forms mentioned.
Furthermore, in the course of practicing a wide variety of commercially important industrial processes, gaseous process streams (or more generally “gaseous streams”) are produced which are contaminated with pernicious quantities of mercury. Here again, the mercury contaminants have proved to be particularly difficult to remove or reduce to acceptable levels. One of the most pernicious forms of mercury pollution in such gaseous streams is finely aerosolized elemental mercury. This form of mercury is generated by coal-fired power generation and is present in natural gas. In the U.S., coal-fired power plants are the largest source of man-made mercury emissions to the air, accounting for approximately 40% of all mercury emissions. Under current circumstances, mercury is adsorbed on the aerosolized soot from coal burning. This soot eventually settles and the mercury adsorbed on the carbon is converted to methyl mercury, dimethyl mercury, and other forms, which accumulate in the food chain. Alternatively, techniques have been developed which will cause the carbonaceous soot to auto-ignite and convert to CO2 and H2O. When this occurs, finely aerosolized elemental mercury is produced. The mechanism for conversion of elemental mercury to methyl mercury and other forms is not well understood, but is most certainly microbially mediated. It is estimated that 2000 tons of mercury is generated this way annually. Elemental mercury also occurs in natural gas in concentrations up to hundreds of micrograms per Nm3. This is a significant amount considering that a typical plant will process millions of Nm3 per day.
Characterization of the Hg species is therefore critical in designing remediation technology, as the three primary forms of mercury (ionic, organically-bound, and elemental) possess very different physical and chemical properties. However, up to now, the ability to characterize mercuric species has been limited and difficult. The reasons are as follows:
1) Mercury is usually present in very low concentrations (usually 1 ppm or less) and there are usually large fluctuations in influent mercury concentration; rendering inaccurate spot sampling;
2) The composition of speciation changes when these small amounts of mercury come in contact with the sample vessel; and
3) Standard tests are destructive and do not differentiate adequately between the three forms.